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July 9, i946. w. D. HERSHBERGER 2,403,527 PULSE-ECHO DISTANCE INDICATOR Filed Jan. 5o, 194s "VVVVV En@ Nm ¿nä Bmnentor Cîttorneg 2,403,527 Patented July 9, 1946 UNITED STATES PATENT OFFICE 2,403,527 PULSE-ECHO DISTANCE INDICATOR William D. Hershberger, Princeton, N. J., assignor to Radio Corporation of America, a corporation o! Delaware Application January so, 1943, serial No. 474,159 7 Claims. (ci. 25o-1) 2 l My invention relates to pulse-echo systems for The invention will be better understood from indicating the presence of or the distance to the following description taken in connection with the accompanying drawing in which reflecting objects. The invention will be described as applied to radio locator apparatus which transmits short periodically recurring radio pulses and which re ceives these pulses after they are reflected from a reflecting object or surface. It is well known that the distance to the reflecting object or sur face can be determined by measuring the time interval that has elapsed between the transmis sion of a pulse and the reception of’ the reflected Figure 1 is a block diagram of one embodi ment of the invention; Figure 2 is a group of graphs which are referred to in explaining the invention; and Figure 3 is a circuit diagram of a phase shifter that may be employed in the apparatus of Fig. 1. In the several figures simi lar parts are indicated by similar reference char acters. In Fig. 1 the invention is shown applied to a pulse. This time interval is commonly measured radio altimeter which comprises a sine wave os cillator I0, a wave shaper I I for producing pe by means of a cathode ray indicator tube. riodic pulses 5, and a keyer I 2 for modulating An object of the present invention is to pro or keying a high frequency radio transmitter I3 vide in a pulse-echo system a method of and by the pulses 5 whereby pulses of radio frequency means for producing an indication when the dis energy are radiated to the reflecting object or tance to a reñecting object or surface falls out side of predetermined distance limits. surface. In the case of an altimeter mounted A further object of the invention is to provide 20 on an aircraftto give an indication of an ob an improved indicator for a radio altimeter of stacle ahead as well as an indication of alti the pulse-echo type. tude, the radiation of the pulses is downward and ~ _ A still further object of the invention is to provide an improved distance indicator for a forward. The reflected pulses are received and demodu pulse-echo system. 25 lated by a receiver I6. The resulting pulses, in dicated at I1, are supplied to an amplifier Ii! In one preferred embodiment of the invention which is connected to energize an indicator lamp a radio altimeter is provided with two indicat ing devices (two lamps, for example) which are I9, and to an amplifier 2| which is connected to energize an indicator lamp 22. The ampli connected to receive the reflected pulses from two amplifiers, respectively, under certain condi 30 fiers I8 and 2| are normally biased to cut-off tions. These amplifiers are normally biased to so that the received pulses I 1 will not energize cut-ofi’ but are rendered operative periodically the indicator lamps I9 and 22 unless the positive at such intervals that the lamps are lighted only pulses 23 and 24 are being impressed upon the amplifiers I 8 and 2 I, respectively. Negative pulses when the altitude is less than a predetermined altitude limit or when the altitude or the distance 35 5' may be supplied to the receiver I6 over a to a reflecting surface is greater than a predeter conductor 20 to make it insensitive during the mined altitude or distance limit and within the transmission of a pulse. Referring to Fig. 2, the positive rectangular range of the altimeter. The latter condition isì encountered either when the aircraft exceeds a pulses '23 are initiated by the transmitter key predetermined altitude or when there is an ob 40 ing pulses 5 and last for an adjustable period fol stagëe such as a mountain in the path of the air lowing the transmitted pulse. The positive rec tangular pulses 24 are initiated at an adjustable The above-mentioned periodic biasing or key time after the termination of the pulses 23 and ing of the amplifiers may be accomplished by last until the occurrence of the next transmit applying positive rectangular voltages thereto 45 ter keying pulse 5. It will be apparent that if from trigger amplifiers or multivibrators. The the reñected pulses arrive at the receiver at a output from one trigger amplifier renders the time between the end of a pulse 23 and the start amplifier for one lamp operative for a short pe of a pulse 24, neither of the indicator lamps I9 riod immediately following the transmission of a and 22 will be lighted. If' lamp I9 lights, it in 50 pulse while the output from the other trigger am.. dicates that the aircraft is too low; if lamp 22 plißer renders the amplifier for the other lamp lights, it indicates either that the aircraft is too operative for a short period immediately preced high or that there is an obstacle ahead. ing the transmission oi’ a pulse. Between these The rectangular pulses 23 and 24 may be ob two periods the reception of a reflected pulse will tained by supplying signal from the sine wave os not light either one of the indicator lamps. cillator I0 to the adjustable phase Shifters 3| and cra . 2,408, 527 32 (one of which is shown in detail in Fig. 3). The sine wave signals from the phase shifters 3| and 32 are supplied to suitable wave shapers 33 and 34, respectively, to produce voltage pulses, indicated at 38 and 31, which have a repetition rate equal to the frequency of the sine wave sig nals. Suitable wave shapers are well known and may comprise, for example, a clipping tube or tubes for changing the sine waves to waves that are substantially rectangular, a diiferentiating circuitl for obtaining narrow pulses from the sub stantially rectangular waves, and additional clip ping means. cannot tell from this alone whether he has ex ~ ceeded the upper limit of altitude or is approach ing an obstacle. This can be checked quickly. l however, by adjusting the phase shifter 3l to see what the altitude actually is, and, if necessary, by also adjusting the phase shifter 32 to ilnd the distance to the reflecting surface that has caused the lamp 22 to light. I claim as my invention: l. A pulse-echo system comprising means i'or transmitting pulses, means for receiving said pulses after reilection from a surface nr object, a pair of indicating devices, means for supplying the received pulses to said indicating devices. amplifiers or multlvibrators 38 and 38, respec means for producing two- groups oi' control pulses tively, at the proper .points so that pulse 36 termi having a deilnite phase relation with respect to nates the rectangular pulse 23 produced by trig the transmitted pulses, and means responsive to ger ampliiler 38, and so that pulse 31 initiates the said two groups of control pulses for making said rectangular pulse 24 produced by trigger ampliiler indicating devices eiîective, respectively, to pro 38. The time relation between the several pulses 20 duce an indication only during a predetermined is shown in Fig. 2. The start of the pulse 23 and period following the transmission of a pulse and ' The pulses 36 and 31 are impressed upon trigger the termination oi' the pulse 24 are determined . by the keying pulse 5 which may be supplied from the wave shaper Il over a conductor 4| to an indication only during a predetermined period ‘ phase shift may be obtained by means of a re ducing control pulses of positive polarity having preceding the transmission of a pulse. 2. The invention according to claim 1 wherein the trigger ampliñers 38 and 39. The time re 25 means is provided for adjusting the widths of lations between the pulses 23 and 24 and the pulse the control pulses in said two groups. 5 are shown in Fig. 2. 3. A pulse-echo system comprising means for The phase Shifters 3| and 32 may be of the transmitting periodically recurring pulses, means type shown in Fig. 3 in which inductance coils/46 for receiving said pulses after reilection from a and 4"l are placed so the axis of coil 48 makes an 30 surface or object, an indicating device, means in angle of 90 degrees with the axis of coil 41 and cluding an amplifier for supplying the received have signals applied to them 90 degrees out of pulses to said indicating device, said amplifier phase to produce a. rotating iield. The 90 degree normally being biased to cut-ofi', means for pro sistor-capacitor network comprising resistors 5| 35 a deiinite phase relation with respect to the trans and 52 and capacitor’53. A rotatably adjustable mitted pulses. means for adjusting the duration pickup coil 48 is mounted in the rotating field of said control pulses, and means for applying whereby the desired phase relation of input sig said positive control pulses to said amplifier to nal to output signal may be obtained by turning make it eilective to pass the received pulses to a phase adjustment knob 3i'. said indicating device for the duration of each It will be apparent that the time of occurrence of the pulses 3B and 31 may be advanced or re control pulse. f 4. A pulse-echo system comprising means for tarded by changing the adjustments of the phase transmitting perodically recurring pulses, means Shifters 3| and 32, respectively. Thus, as indi for receiving said pulses after reñection from a cated by the dotted line portions of the graphs 45 surface or object, an indicating device, means in Fig. 2, the duration of the pulse 23 may be in including an amplifier for supplying the received creased or decreased to determine the lower al titude limit at which the indicator lamp i9 will light, and the starting time of the pulse 24 may be changed to determine the upper altitude or dis tance limit at which the indicator lamp 22 will light. Therefore, as previously stated, one indi cator will give a warning signal when the altitude of the aircraft is below a predetermined adjusta ble limit and the other indicator will give a warn pulses to said indicating device, said ampliiler normally being biased to cut-olf, means for pro ducing control pulses having a known phase re lation with respect to the transmitted pulses. means for adjusting the phase of said control pulses with respect to the transmitted pulses, means for producing positive control pulses hav ing a duration which is determined by the phas ing oi’ said control pulses, and means for ap ing when the altitude is above a predetermined adjustable limit or when an obstacle is being approached. 'I'he phase Shifters 3| and 32 preferably are cal ibrated in distance so that the distance to the plying said positive control pulses to said am plitler to make it effective to pass the received pulses to said indicating device for the duration of each control pulse. reñecting surface may be found by rotating the transmitting pulses, means for receiving said phase adjustment knobs 3 I ' or 32', respectively, to the point where the indicator lamps I9 or 22, re spectively, either light up if previously dark or extinguish if previously lighted. For example, the altitude may be determined by adjusting the phase shifter 3| until the lamp i9 blinks on and oil’ when the knob 3|’ is rotated left and right very slight amounts. The pointer on knob 3|' ‘ 5. A pulse-echo system comprising means for pulses after reflection from a surface or object, a pair of indicating devices, means including a pair of ampli?ers for supplying the received pulses to said pair of indicating devices, respec tively, said ampliñers normally being biased to 'cut-ofi’. means for producing two groups oi.' con trol pulses of positive polarity having a known phase relation and duration with respect to the theln shows the altitude reading on the associated 70 transmitted pulses, means for adiusting the dura sca e 6. . tion of said control pulses with respect to the Similarly the altitude may be determined by transmitted pulses, and means for applying said adjusting the phase shifter 32 and reading the two groups of positive control pulses to said am~ distance on' the scale 1. It may be noted that pliners. respectively, to make them eiïective to if, when in llight, the lamp 22 lights. the pilot pass the received pulses to said indicating de 2,463,527 viäles for the duration ot each applied control p se. 6. A pulse receiver for a system that includes means for transmitting pulses. said receiver com prising means for receiving said transmitted pulses after they have been reilected from a 6 prising means for receiving said transmitted pulses after they have been reñected from a surface or object, two indicating devices; means for supplying the received pulses to said indicat ing devices, means for producing control pulses that occur immediately following the transmis surface or object, indicating means, means for sion of a pulse, means for producing second con sion of a pulse, means for producing second con certain period between a iirst control pulse and the following second control pulse, means re trol pulses that occur immediately preceding the supplying the received pulses to said indicating transmission of a pulse but after the termina means, means for producing iìrst control pulses that occur immediately following the transmis 10 tion oi the iirst control pulses whereby there is a trol pulses that occur immediately preceding the transmission of a pulse but after the termina sponsive to said iirst control pulses for causing one of said indicating devices'to indicate when tion oi the ilrst control pulses, and means respon sive to said first and second control pulses for 15 the reflected pulses are received during the oc currence of the iirst control pulses, and means causing said indicating means to indicate whenl responsive to said second control pulses for caus the reil‘ected pulses are received during the oc ing the other of said indicating devices to indicate currence of either the first control pulses or the when the reflected pulses are received during the second control pulses. '1. A pulse receiver for a system that includes 20 occurence of the second control pulses. ' WILLIAM D. HERSHBERGER. means ior transmitting pulses, said receiver com Disclaimer N. J. PULSE-Echo Drs'rsNcr:y 2,403,527.-Wül1'am D. Hershberger Princeton, 1946. Disclaimer filed Nov. 5, 1949, INDICATOR. Patent dated ‘ uly 9, by the assignee, Radio Corporation 0j America. Hereb enters this disclaimer to claims 3 and 4 of said patent. [ ° Gazette DecemberI 27, 1949.] , '